The 3D printed technology provides a way to create untraceable guns without serial numbers and without the owner needing a background check, things gun control advocates say are risky.
A USA federal judge in Seattle has blocked the release of software that allows consumers to 3D-print firearms.
A Texas company called Defense Distributed is now fighting a legal battle over publication of plans which would allow gun lovers to print out firearms including a replica of the notorious AR-15 assault rifle, which has been used in a number of mass shootings. The judge sided with Washington and other states, which sought the restraining order.
Trump said he's spoken with the National Rifle Association about the so-called ghost guns, although the gun lobby hasn't directly weighed in on the issue.
He says the company said in court it actually began distributing gun files Friday and by Sunday, 1,000 people had downloaded 3D plans for AR-15 semi-automatic assault rifles.
Outrage over the administration decision is putting gun control back into the election-year political debate, but with a high-tech twist.
"We don't agree with President Trump very much", Washington state Assistant Attorney General Jeff Rupert told Lasnik, "but when he tweeted 'this doesn't make much sense, ' that's something we agree with".
Trump spoke after eight states filed suit against the administration, contending the hard-to-trace plastic weapons are a boon to terrorists and criminals and threaten public safety. "The vast majority of 3D printed gun designs are not undetectable to metal detectors".
Senator Edward Markey of MA, a Democrat, said Trump has boasted that he alone can fix problems afflicting the country.More news: Mitrovic returns to Fulham after brilliant loan spell
"We were disappointed in the ruling and view it as a massive prior restraint of free speech", Blackman said.
"I am looking into 3-D Plastic Guns being sold to the public", the president tweeted. If you want your Second Amendment online.
Kenneth Schwartz reported this story for VOA News.
A 1988 federal law - drafted with NRA support - barred the manufacture, sale or possession of an undetectable firearm.
Markey, Blumenthal and other Democrats filed legislation that would prohibit the publication of a digital file online that allows a 3D printer to manufacture a firearm.
He noted that there have always been computer-driven machines used to manufacture products out of metal, which would make more durable guns than the hard plastic ones 3D printers churn out.
The settlement followed a long legal battle between self-described anarchist Cody Wilson, 30, Defense Distributor's founder, and the department.
The proliferation of such firearms could also take business away from the traditional gun industry, the companies that the NRA represents, and confound law enforcement in attempts to reduce gun violence or get illegal guns off the street. State Department officials said the plans violated US export laws.
"It's another one of those new technologies that the police just have to keep apace of and be one step ahead of people who are going to use them for criminal activity".